Some types of flat panel display devices are TFT-LCDs (Thin Film Transistor-Liquid Crystal Displays), EL (Electro Luminance) displays, STN (Super Twisted Nematic)-LCDs, and PDPs (Plasma Display Panels).
FIG. 1 is a block diagram of a conventional TFT-LCD 100 that includes a TFT-LCD panel 110 and peripheral circuits. The TFT-LCD panel 110 includes an upper plate and a lower plate, each including a plurality of electrodes for forming electric fields, a liquid crystal layer between the upper and lower plates, and polarization plates for polarizing light which are respectively attached to the upper and lower plates. The brightness of light that is transmitted through the TFT-LCD 100 is controlled by applying corresponding voltages (gray voltages) to pixel electrodes to re-arrange liquid crystal polymers in the liquid crystal layer and cause various gray levels. To apply the gray voltages to the pixel electrodes, a plurality of switching devices, such as TFTs, connected to the pixel electrodes are located on the lower plate of the TFT-LCD panel 110. The switching devices (e.g., TFTs) control the brightness (transmissivity) of light through a pixel area and, for color displays, three colors (e.g., R (Red), G (Green), and B (Blue)) can be formed through a pixel array with a color filter arrangement, such as that shown in FIG. 2.
The TFT-LCD 100 includes gate drivers 120 for driving a plurality of gate lines arranged horizontally and source drivers 130 for driving a plurality of source lines arranged vertically. The source and gate lines are arranged on the LCD panel 110. The gate and source drivers 120 and 130 are controlled by a controller (not shown). Generally, the controller is provided outside the LCD panel 110. The gate and source drivers 120 and 130 are generally located outside the LCD panel 110, however, they can be located on the LCD panel 110 in a COG (Chip On Glass) display.
FIG. 3 is a block diagram of a conventional source driver 130. Referring to FIG. 3, the conventional source driver 130 includes a plurality of gamma decoders 131 and buffers 132. Each gamma decoder 131 receives n bits of image data (n=6, 8, 10, . . . ), and selects and outputs an analog voltage corresponding to a digital value of the image data among 2n analog gray voltages. The image data is digital data obtained by processing a three-color signal (e.g., RGB digital data) transmitted from an external source such as a graphics card in the controller according to a resolution of the LCD panel 110. Analog image signals output from the gamma decoders 131 are buffered by the corresponding buffers 132 and respectively output to source lines S1, S2, S3, S4, etc. The analog image signals output from the buffers 132 quickly charge the source lines S1, S2, S3, S4, etc. and corresponding pixels on the LCD panel 110. Liquid crystal molecules of the pixels receiving the image signals are re-arranged in proportion to applied gray voltages, and thereby control the brightness of light transmitted therethrough.
To enhance color reproducibility by increasing the number of bits of R, G, and B image data, the area of a gamma decoder circuit used to decode the bits can increase in proportion to the increased number of bits. To avoid such increase in circuit complexity, an amplifier interpolation scheme has been developed. According to one such amplifier interpolation scheme, representative gray voltages are selected based on upper bits of digital image data and intermediate values are created from the selected representative gray voltages based on the remaining lower bits. The amplifier interpolation scheme can use a half method capable of reducing the gamma decoder circuit area by ½ or a quarter method capable of reducing the area by ¾. In the half method, intermediate interpolated voltages are created from representative gray voltages selected based on the upper bits of input image data. In the quarter method, interpolated voltages with ¼ the interval of representative gray voltages selected based on the upper bits of input image data are created.
This conventional amplifier interpolation scheme depends on input voltages of an amplifier used for interpolation. Interpolation of the voltages can become skewed if differences between input voltages of the amplifier are not small or if the differences are not equal for all gray levels. Accordingly, a source driver that uses the conventional interpolation scheme may not create interpolated voltages that enable generation of stable and uniformly distributed gray level differences.